Field
Embodiments of the invention relate to sensing and control schemes for a gyroscope based on signal phase.
Background
Microelectromechanical systems (MEMS) are miniature devices composed of one or more mechanical components coupled with an integrated circuit (IC). A MEMS gyroscope (or gyro) is a MEMS device that is designed to measure angular rate. For example, a sufficiently accurate gyro would be able to measure the rate of rotation of the earth (˜15 deg/hr). MEMS gyros are becoming more and more ubiquitous in consumer electronics such as cell phones, tablets, cameras, etc. To be included in such applications, a gyro must adhere to stringent requirements regarding power consumption, physical size, and performance.
MEMS gyros typically contain a miniature mechanical resonator with multiple vibrational degrees-of-freedom called modes. A tri-axial MEMS gyro may contain one drive-mode and three sense-modes. In such a device, the drive-mode is driven into resonance at its characteristic frequency with a driving actuator, and the motion of three sense-modes, oriented in orthogonal directions such as roll, pitch, and heading, are measured with sensing transducers. When exposed to an externally applied angular rate, some of the oscillatory motion of the drive-mode causes one or more of the sense-modes to oscillate mechanically. Thus, angular rate can be determined through measurement of the motion of the sense-modes. An example providing the design of a MEMS gyroscope may be found in U.S. Pat. No. 6,626,039, the disclosure of which is incorporated by reference herein in its entirety.
The overall signal-to-noise (S/N) of a MEMS gyro is largely dictated by the dynamic range and noise characteristics of the analog front-end (AFE) circuitry. In general, decreasing the AFE noise requires increased power consumption. Thus, MEMS gyros usually exhibit a trade-off between power consumption and performance. A MEMS gyro AFE typically consists of an amplifier front-end with a high-impedance feedback network, providing high gain. Resistive feedback networks provide simple passive networks, but suffer from thermal noise. Switched-capacitor networks must be actively reset and suffer from noise folding effects similar in magnitude to resistor thermal noise. Regardless of the feedback network of choice, the output is at best limited to the supply voltage rails of the amplifier (Vss, Vdd), ultimately limiting the achievable dynamic range.